Shimano Deore XT Centerlock Bicycle Hydraulic Disc Brake - SM-RT81 - 140mm, 160mm,180mm, 203mm Material: [rotor] steel, [carrier] aluminum Attachment Type: centerlock Compatibility: Shimano disc brakes, centerlock hubs Diameter: 160mm, 180mm Claimed Weight: [160mm] 122g, [180mm] 149g